TMET-42. Fluid-suppressed APTw-CEST MRI enhances tumor-edema differentiation in malignant brain tumors

Abstract BACKGROUND Conventional Magnetic Resonance Imaging (MRI) struggles to distinguish tumor recurrence from non-neoplastic treatment-related changes (TRC) in patients with brain tumors. Amide Proton Transfer-weighted (APTw) imaging is a molecular Chemical Exchange Saturation Transfer (CEST) -based MRI technique to detect changes in mobile protein content, elevated in brain tumors. Standard APTw-CEST relies on Magnetization Transfer Ratio Asymmetry (MTRasym) metrics, which can be confounded by peritumoral edema. The purpose of this study was to optimize APTw-CEST imaging by applying fluid-suppression post-processing metrics to enhance contrast between tumor tissue and surrounding edema. METHODS Following IRB approval, conventional APTw-CEST protocol (2D fast spin-echo; 2μT saturation power; 2s saturation time; 1.6×2.2 mm² spatial resolution; 30 offsets; GE 3T PET/MRI system) was acquired in patients with glioma (N=5) or brain metastases (N=3) following treatment when the MRI was equivocal for tumor recurrence vs TRC. The Olea Sphere 3.0 software suite was employed for data denoising, motion correction, and B0 correction. Finally, conventional APTw maps were generated using the MTRasym metric, and fluid-suppressed APTw maps were computed using the MTRRex metric, both quantified at 3.5 ppm relative to the water resonance. All results were validated with pathological tissue confirmation. RESULTS APTw-CEST imaging of patients with path-proven tumor recurrence (N=4) achieved a mean %APTw-CESTΔ=2.17 (range: 1.68 to 2.7). Application of fluid-suppressed APT-CEST in the same patients yielded a mean %APTw-CESTΔ =1.43 (range: 1.14 to 2.13). Patients with path proven TRC (N=4) had a non-fluid suppressed %APTw-CESTΔ mean=0.18 (range: -0.27 to 0.76) and fluid-suppressed % APTw-CESTΔ mean=0.18 (range -0.17 to 0.63). An optimal fluid suppressed %APT-CESTΔ cutoff of 1.1 allowed full discernment of tumor relapse from TRC. CONCLUSION Fluid-suppressed APTw-CEST imaging in a small sample of patients with malignant brain tumors enhanced image quality, reduced peritumoral edema, and aided in differentiation between progression and treatment-induced changes. This advancement can enhance clinical utility of APTw-CEST, providing a more reliable approach for evaluating brain tumor recurrence.